RV FEATURE
DUTY CYCLE
Not all electrical devices run continuously . Many , like fridges and air-conditioners , are set to operate at a certain temperature and they maintain that by periodically switching on and off . This is called a duty cycle . It means that , even though a device is rated at , say , 1000W , it may only operate at half that in watt hours over time .
This will vary depending on the conditions and the device settings . Estimating their actual power usage over time is almost impossible . My advice would be to use 75 per cent of their rated output as a safe estimate .
Therefore , when calculating the power consumption of a caravan fridge rated at 100W , assume a duty cycle of around 75Wh .
This Simarine battery monitor provides the net wattage going in or out of your battery as well as the battery state of charge and time to discharge .
REAL WORLD USAGE
This is all good in theory , but how does it work in the real world ? Again , this is a great question . When we look at the overall operation of our electrical system , we see the benefit of breaking everything down to watts .
When you ’ re free-camping in your RV , power will be flowing in both directions . You will have power going out of your battery to operate your appliances , and you will have power coming in from your solar panels or perhaps a generator running your battery charger . Depending on the situation , you will have a net power flow either to or from the battery and , knowing this , you can estimate how much time you have left to either recharge or flatten them .
Going back to our 100Ah battery , which we have already ascertained is a 1200Wh battery , running a 1000W air-conditioner while simultaneously receiving 500W of solar charging , how long will the air-conditioner run before the batteries run flat ?
We calculate our net charge / discharge rate by subtracting the solar panel charge from the load usage : 500Wh minus 1000Wh equals 500Wh net discharge .
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